Clemens, in U.S. Pat. No. 3,842,194, has disclosed a system for recording and playback of information, including audio, video and color information, capacitively. A high density information disc has signal information in the form of a surface relief pattern in an information track, e.g., a spiral groove on the surface of the disc. The disc is made conductive with a metal layer, which acts as the first electrode of a capacitor, and then with a dielectric layer. The disc is played back by means of a stylus electrode which is the second electrode of the capacitor. An application of this invention is the capacitance electronic disc system. Since the disc is rotated at a fairly high speed, on the order of 450 rpm, the friction between the stylus and the disc surface may result in undue stylus wear. Thus, a lubricant is applied to the surface of the disc.
A suitable class of lubricants has been described by Matthies in U.S. Pat. No. 3,833,408, herein incorporated by reference. These lubricants have the general formula ##STR1## wherein R is an alkyl group of 4 to 20 carbon atoms and n is an integer.
Various improvements have been made to the disc of Clemens including a disc made from a conductive plastic which avoids the need for applying separate conductive metal and dielectric layers. Such a disc may contain conductive particles, for example, either throughout or in a surface layer. Improvement has also been made to the lubricant system. It has been found that when the lubricant is purified and fractionated, improved playback and storage stability results. The fractionated lubricant has the formula ##STR2## wherein R.sub.1 and R.sub.2 are alkyl groups of 4-20 carbon atoms, x is an integer of 2-4 and y is an integer of 0-2 and wherein the sum of x and y is 4 or less. These lubricants are described by Wang et al in U.S. Pat. No. 4,275,101, also incorporated herein by reference.
Some problems still remain for the lubricated disc. The disc surface has been found to be sensitive to moisture; that is, when the disc is exposed to ambient conditions over a period of time, particularly including conditions of high relative humidity, a thin layer of organic and inorganic water soluble salt deposits form on the surface of the disc, lifting the stylus during playback and interrupting the signal. This loss of signal has been termed "carrier distress". This carrier distress has been alleviated somewhat by careful cleaning and drying of the disc surface which removes water soluble materials that have formed on the surface during molding operations. However, with time, additional water soluble materials and external debris form on the surface of the disc, particularly in the presence of water vapor. Further, this requirement of cleaning and drying of the discs adds to the cost of manufacture. It would be desirable to eliminate this extra processing of the disc.
Thus, more recently, the fractionated methyl alkyl siloxane lubricant has been doped with various materials including hydroxylated amines and polar silicones which have improved the resistance of the disc surface to carrier distress. We have insufficient knowledge at the present time about the nature of the disc surface to predict which materials will be effective in reducing susceptability of the disc to degeneration from high temperature, high relative humidity conditions.
Polyphenylene ether (PPE) lubricants as a class have improved resistance to oxidation, moisture and shear stress. Also, they are far less expensive than the fractionated methyl alkyl siloxane lubricants currently being used. Further, although the exact mechanism of lubrication of high density information discs is not known, it is known that the surface of these discs and the polyphenylene ether lubricants are highly polar which provides excellent adhesion of these lubricants to the disc surface. However, the high surface tension of the polyphenylene ether prevents successful wetting and complete coverage of the disc surface by this lubricant. It is necessary to modify the high surface tension of the polyphenylene ether for improved wetting of the disc's surface to make the polyphenylene ether effective for high density information disc lubrication.